Rotation induction device for vehicle

ABSTRACT

A rotation induction device for a vehicle includes: an upper case formed of a synthetic resin material, and having a piston rod passing therethrough; a lower case formed of a synthetic resin material and disposed under the upper case, wherein the piston rod passes through the lower case; a center plate formed of a synthetic resin material, disposed between the upper case and the lower case such that the piston rod passes through the center plate, and configured to induce rotation of either one or both of the upper case and the lower case; and a ring-shaped installation space disposed between the upper and lower cases, wherein the center plate is inserted in the ring-shaped installation space.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit under 35 U.S.C. § 119(a) of KoreanPatent Application No. 10-2020-0107112 filed on Aug. 25, 2020 in theKorean Intellectual Property Office, the entire disclosure of which isincorporated herein by reference for all purposes.

BACKGROUND Field

Exemplary embodiments of the present disclosure relate to a rotationinduction device for a vehicle, and more particularly, to a rotationinduction device for a vehicle, which includes a bearing that is usedfor a suspension of a vehicle and made of synthetic resin, in order toimprove operability.

Discussion of the Background

In general, a strut-type suspension is used for a front wheel of afour-wheel vehicle having a structure in which a coil spring is combinedwith a strut assembly having a hydraulic shock absorber embedded in anouter shell integrated with a main shaft. The strut-type suspension isdivided into a suspension in which a piston rod of the strut assembly isrotated when the strut assembly is rotated with the coil spring during asteering operation, and a suspension in which the piston rod of thestrut assembly is not rotated when the strut assembly is rotated withthe coil spring during the steering operation. In order to smoothlyallow the rotation of the strut assembly in any strut-type suspension, abearing is used between a mounting member of a vehicle body and an upperspring support sheet of the coil spring.

As the bearing, a rolling bearing using a ball or needle is used.However, the rolling bearing has a problem in that fatigue fraction mayoccur in the ball or needle due to a vibration load or slight rolling,which makes it difficult to maintain a smooth steering operation.Therefore, there is a need for a device capable of solving the problem.

The related art of the present disclosure is disclosed in Korean PatentApplication Publication No. 2020-0033219 published on Mar. 27, 2020 andentitled “Strut Bearing Assembly for Suspension”.

SUMMARY

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used as an aid in determining the scope of the claimed subjectmatter.

In one general aspect, a rotation induction device for a vehicleincludes: an upper case formed of a synthetic resin material, and havinga piston rod passing therethrough; a lower case formed of a syntheticresin material and disposed under the upper case, wherein the piston rodpasses through the lower case; a center plate formed of a syntheticresin material, disposed between the upper case and the lower case suchthat the piston rod passes through the center plate, and configured toinduce rotation of either one or both of the upper case and the lowercase; and a ring-shaped installation space disposed between the upperand lower cases, wherein the center plate is inserted in the ring-shapedinstallation space.

The upper case may include: an upper cover part configured to cover atop of the center plate, the upper cover part having an upper holeformed in a center thereof such that the piston rod passes through theupper hole; and an upper blocking part disposed at an edge of the uppercover part, and configured to block an inflow of foreign matter.

The lower case may include: a lower cover part configured to cover abottom of the center plate, the lower cover part having a lower holeformed in a center thereof such that the piston rod passes through thelower hole; and a lower blocking part disposed at an edge of the lowercover part, and configured to block the inflow of foreign matter.

The upper blocking part may include: an upper blocking hook partextended downward from the edge of the upper cover part; and an upperblocking protrusion part protruding downward from the upper cover part,and disposed to face the upper blocking hook part.

The lower blocking part may include: a lower blocking locking partdisposed at the edge of the lower cover part, and including a groove towhich the upper blocking hook part is locked and fixed; a lower blockingdropping part extended from the edge of the lower cover part toward abottom of the upper blocking hook part and configured to drop foreignmatter; and a lower blocking protrusion part protruding upward from theedge of the lower cover part, and disposed between the upper blockinghook part and the upper blocking protrusion part.

The center plate may include: a center disk part; a center innercircumferential part formed on an inner circumferential surface of thecenter disk part; a center outer circumferential part formed on an outercircumferential surface of the center disk part; a center upper curvedpart formed at a top of the center disk part, and disposed in linecontact with the upper case; and a center lower curved part disposed ata bottom of the center disk part, and disposed in line contact with thelower case.

Tops of the center inner circumferential part and the center outercircumferential part may be located at a level higher than a top surfaceof the center disk part. Bottoms of the center inner circumferentialpart and the center outer circumferential part may be located at a levellower than a bottom surface of the center disk part.

The center upper curved part and the center lower curved part may eachhave one or more cycloid surfaces.

A lubricant may be disposed in a curved storage part disposed betweenthe one or more cycloid surfaces.

A volume of the center plate may be 50% to 98% of a volume of theinstallation space.

The center plate may include: a cycloid upper surface in contact with alower surface of the upper case; and a cycloid lower surface in contactwith an upper surface of the lower case.

Other features and aspects will be apparent from the following detaileddescription, the drawings, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram schematically illustrating that a rotation inductiondevice for a vehicle in accordance with an embodiment of the presentdisclosure is installed.

FIG. 2 is a diagram schematically illustrating the rotation inductiondevice for a vehicle in accordance with the embodiment of the presentdisclosure.

FIG. 3 is a diagram schematically illustrating an upper case and a lowercase in accordance with an embodiment of the present disclosure.

FIG. 4 is a diagram schematically illustrating a friction restraint partin accordance with an embodiment of the present disclosure.

FIG. 5 is a diagram schematically illustrating a position guide part inaccordance with an embodiment of the present disclosure.

FIG. 6 is a diagram schematically illustrating a lubricant retentionpart in accordance with an embodiment of the present disclosure.

FIG. 7 is a diagram schematically illustrating a center plate inaccordance with an embodiment of the present disclosure.

FIG. 8 is a diagram schematically illustrating an installation space inaccordance with an embodiment of the present disclosure.

FIG. 9 is a diagram schematically illustrating an inflow prevention partin accordance with an embodiment of the present disclosure.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Hereinafter, a rotation induction device for a vehicle will be describedbelow with reference to the accompanying drawings through variousexemplary embodiments. It should be noted that the drawings are not toprecise scale and may be exaggerated in thickness of lines or sizes ofcomponents for descriptive convenience and clarity only. Furthermore,the terms as used herein are defined by taking functions of theinvention into account and can be changed according to the custom orintention of users or operators. Therefore, definition of the termsshould be made according to the overall disclosures set forth herein.

FIG. 1 is a diagram schematically illustrating that a rotation inductiondevice for a vehicle in accordance with an embodiment of the presentdisclosure is installed, and FIG. 2 is a diagram schematicallyillustrating the rotation induction device for a vehicle in accordancewith the embodiment of the present disclosure. Referring to FIGS. 1 and2 , the rotation induction device 1 for a vehicle in accordance with theembodiment of the present disclosure includes an upper case 10, a lowercase 20 and a center plate 30.

The upper case 10 is made of a synthetic resin material, and has apiston rod 200 disposed therethrough. For example, the upper case 10 mayhave a hole formed in the center thereof such that a piston rod 200passes through the hole, and an insulator 300 may be disposed above theupper case 10.

The lower case 20 is made of a synthetic resin material, and disposedunder the upper case 10 such that the piston rod 200 passes through thelower case 20. For example, the lower case 20 may have a hole formed inthe center thereof such that the piston rod 200 passes through the hole,and a sheet 500 to support the top of a spring 400 may be disposed underthe lower case 10.

The center plate 30 is made of a synthetic resin material, and disposedbetween the upper case 10 and the lower case 20 such that the piston rod200 passes through the center plate 30. Such a center plate 30 inducesthe rotation of any one of the upper and lower cases 10 and 20. Forexample, the center plate 30 may retain the state in which the topsurface thereof is contacted with the upper case 10 and the bottomsurface thereof is contacted with the lower case 20. The center plate 30may induce the contact surfaces to slide, thereby inducing the rotationof the lower case 20.

FIG. 3 is a diagram schematically illustrating the upper case and thelower case in accordance with an embodiment of the present disclosure.Referring to FIGS. 2 and 3 , the upper case 10 includes an upper coverpart 11 and an upper blocking part 12, and the lower case 20 includes alower cover part 21 and a lower blocking part 22.

The upper cover part 11 has an upper hole 111 formed in the centerthereof, such that the piston rod 200 passes through the upper hole 111.The upper cover part 11 covers the top of the center plate 30. Forexample, the upper cover part 11 may be formed in a ring shape throughwhich the piston rod 200 can pass.

The upper blocking part 12 is formed at the edge of the upper cover part11, and serves to block the inflow of foreign matters. For example, theupper blocking part 12 may be integrated with the upper cover part 11,and induce foreign matters to fall down while fluid introduced from theoutside is moved upward and downward.

The lower cover part 21 has a lower hole 211 formed in the centerthereof, such that the piston rod 200 passes through the lower coverpart 21. The lower cover part 21 covers the bottom of the center plate30. For example, the lower cover part 21 may be formed in a ring shapethrough which the piston rod 200 passes.

The lower blocking part 22 is formed at the edge of the lower cover part21, and serves to block the inflow of foreign matters. For example, thelower blocking part 22 may be integrated with the lower cover part 21,and serve to induce the coupling with the upper blocking part 12.Furthermore, the lower blocking part 22 may be spaced apart from theupper blocking part 12, and thus drop foreign matters while guidingfluid.

More specifically, the upper blocking part 12 includes an upper blockinghook part 121 and an upper blocking protrusion part 122.

The upper blocking hook part 121 is extended downward from the edge ofthe upper cover part 11. For example, the upper blocking hook part 121may have a lower end formed in a hook shape so as to be hooked to thelower case 20.

The upper blocking protrusion part 122 protrudes downward from the uppercover part 11 so as to face the upper blocking hook part 121. Forexample, the upper blocking protrusion part 122 may have an outerdiameter smaller than that of the upper blocking hook part 121.

The lower blocking part 22 includes a lower blocking locking part 221, alower blocking dropping part 222 and a lower blocking protrusion part223.

The lower blocking locking part 221 is formed at the edge of the lowercover part 21, and has a groove to which the upper blocking hook part121 is hooked and fixed. For example, the lower blocking locking part221 may be formed at the outer circumferential surface of the lower case20, and the upper blocking hook part 121 may be inserted into the lowerblocking locking part 221 and then hooked and fixed thereto. Thus, fluidintroduced between the upper blocking hook part 121 and the lowerblocking locking part 221 may flow backward due to the shapes of theupper blocking hook part 121 and the lower blocking locking part 221,which makes it possible to suppress the inflow of foreign matters.

The lower blocking dropping part 222 is extended from the edge of thelower cover part 21 toward the bottom of the upper blocking hook part121, in order to drop foreign matters. For example, the lower blockingdropping part 222 may be extended from the outer lower end of the lowercover part 21, and the upper blocking hook part 121 may be disposedabove the lower blocking dropping part 222.

At this time, the upper blocking hook part 121 has an upper inclinedsurface 125 formed thereon, and the lower blocking dropping part 222 hasa lower inclined surface 225 formed to face the upper inclined surface125. The space between the upper inclined surface 125 and the lowerinclined surface 225 may be so narrow as to suppress the inflow offoreign matters into the lower blocking locking part 221. Since theupper inclined surface 125 is formed on the outer lower end of the upperblocking hook part 121, foreign matters contained in the air introducedbetween the upper blocking hook part 121 and the lower blocking droppingpart 222 may flow downward so as to be discharged to the outside.

The lower blocking protrusion part 223 protrudes upward from the edge ofthe lower cover part 21 so as to be disposed between the upper blockinghook part 121 and the upper blocking protrusion part 122. For example,the lower blocking protrusion part 223 may be extended upward from thetop surface of the edge of the lower cover part 21. The top of the lowerblocking protrusion part 223 may be located at a higher level than thebottom of the upper blocking protrusion part 122. Therefore, themovement of fluid having passed through the lower blocking protrusionpart 223 may be restricted by the upper blocking protrusion part 122,such that foreign matters are dropped.

Therefore, the inflow of foreign matters between the upper blocking part12 and the lower blocking part 22 may be suppressed, and the foreignmatters may be rapidly dropped through the upper inclined surface 125and the lower inclined surface 225, which makes it possible to preventrotational friction or damage caused by the accumulation of foreignmatters. Furthermore, although fine foreign matters pass through thespace between the upper blocking hook part 121 and the lower blockinglocking part 221, the foreign matters may be caught by the upperblocking protrusion part 122 and dropped down to the top of the lowercover part 21. At this time, when the pair of lower blocking protrusionparts 223 are formed so that the upper blocking protrusion part 122 isdisposed between the lower blocking protrusion parts 223, it is possibleto prevent an increase in rotational friction and part damage caused bythe inflow of foreign matters into the center plate 30.

FIG. 4 is a diagram schematically illustrating a friction restraint partin accordance with an embodiment of the present disclosure. Referring toFIG. 4 , the rotation induction device 1 for a vehicle in accordancewith the embodiment of the present disclosure may further include afriction restraint part 40. The friction restraint part 40 is formed onany one or more of the upper and lower cases 10 and 20, and serves torestrain friction with the center plate 30.

More specifically, the friction restraint part 40 includes an upperrestraint part 41 and a lower restraint part 42.

The upper restraint part 41 is formed on the upper case 10, and broughtinto line contact with the center plate 30. For example, the upperrestraint part 41 may be brought into line contact with the top surfaceof the center plate 30 so as to reduce frictional resistance.

The lower restraint part 42 is formed on the lower case 20, and broughtinto line contact with the center plate 30. For example, the lowerrestraint part 42 may be brought into line contact with the bottomsurface of the center plate 30 so as to reduce frictional resistance.

The upper restraint part 41 and the lower restraint part 42 each havecycloid surfaces. When the upper and lower restraint parts 41 and 42each have the cycloid surfaces, stress concentrated by a vertical loadmay be distributed. The space formed between the cycloid surfaces mayhave a lubricant stored therein. That is, the connection point betweenthe adjacent cycloid surfaces may correspond to the bottoms of thecycloid surfaces, such that a recess is formed therebetween, and alubricant such as grease may be stored in such a recess.

FIG. 5 is a diagram schematically illustrating a position guide part inaccordance with an embodiment of the present disclosure. Referring toFIG. 5 , the rotation induction device 1 for a vehicle in accordancewith the embodiment of the present disclosure may further include aposition guide part 50. The position guide part 50 is formed on any oneor more of the upper and lower cases 10 and 20, and serves to guide theposition of the center plate 30.

More specifically, the position guide part 50 includes an upper guidepart 51 and a lower guide part 52.

The upper guide part 51 protrudes downward from the upper case 10 andsupports the inner circumferential surface of the center plate 30. Forexample, the upper guide part 51 may protrude downward from the bottomsurface of the upper cover part 11, have a circular belt shape, and bedisposed to face the upper blocking protrusion part 122.

The lower guide part 52 protrudes upward from the lower case 20 andsupports the outer circumferential surface of the center plate 30. Forexample, the lower guide part 52 may protrude upward from the topsurface of the lower cover part 21, have a circular belt shape, and bedisposed to face the lower blocking protrusion part 223. At this time,the upper blocking protrusion part 122 may be disposed between the lowerblocking protrusion part 223 and the lower guide part 52.

FIG. 6 is a diagram schematically illustrating a lubricant retentionpart in accordance with an embodiment of the present disclosure.Referring to FIG. 6 , the rotation induction device 1 for a vehicle inaccordance with the embodiment of the present disclosure may furtherinclude a lubricant retention part 60. The lubricant retention part 60may be formed on the lower case 20 so as to form a barrier wall forstoring a lubricant.

More specifically, the lubricant retention part 60 includes a firstlubricant retention part 61 and a second lubricant retention part 62.

The first lubricant retention part 61 protrudes upward from the lowercase 20 and covers the inner circumferential surface of the center plate30. For example, the first lubricant retention part 61 may be extendedupward from the top surface of the lower cover part 21 so as to directlysupport the inner circumferential surface of the center plate 30, ordisposed adjacent to the upper guide part 51 so as to prevent alubricant from overflowing to the inside of the center plate 30.

The second lubricant retention part 62 protrudes upward from the lowercase 20 and covers the outer circumferential surface of the center plate30. For example, the second lubricant retention part 62 may be extendedupward from the top surface of the lower cover part 21, directly supportthe outer circumferential surface of the center plate 30, and prevent alubricant from overflowing to the outside of the center plate 30. Thesecond lubricant retention part 62 may be separately formed or replacedwith the lower guide part 52.

At this time, the height (a) of the lubricant retention part 60 may beset in the range of 50% to 60% of the height (b) of the center plate 30.That is, when the first and second lubricant retention parts 61 and 62have the same height, the height (a) of the lubricant retention part 60may be defined as expressed by Equation 1 below.0.5b≤a≤0.9b  [Equation 1]

Through the regulation of the ratio of the height of the lubricantretention part 60, the lower case 20 may serve as a lubricant pocket ofthe center plate 30, and the lubricant retention part 60 may serve as abarrier wall for preventing a lubricant leak, which makes it possible tomaximize the lubrication performance of the lubricant and to reducetorque.

FIG. 7 is a diagram schematically illustrating the center plate inaccordance with the embodiment of the present disclosure. Referring toFIG. 7 , the center plate 30 in accordance with the embodiment of thepresent disclosure is brought into line contact with the upper case 10and the lower case 20, in order to induce rotation.

More specifically, the center plate 30 includes a center disk part 31, acenter inner circumferential part 32, a center outer circumferentialpart 33, a center upper curved part 34 and a center lower curved part35.

The center disk part 31 is disposed between the upper cover part 11 andthe lower cover part 21. For example, the center disk part 31 may beformed in a disk shape with a hole formed in the center thereof. Thecenter disk part 31 may be disposed between the upper guide part 51 andthe lower guide part 52.

The center inner circumferential part 32 is formed on the innercircumferential surface of the center disk part 31. For example, thecenter inner circumferential part 32 may be designed in such a mannerthat the top thereof is located at a higher level than the top surfaceof the center disk part 31 and the bottom thereof is located at a lowerlevel than the bottom surface of the center disk part 31. The centerinner circumferential part 32 may be supported by the upper guide part51 such that the position of the center inner circumferential part 32 ismaintained.

The center outer circumferential part 33 is formed on the outercircumferential surface of the center disk part 31. For example, thecenter outer circumferential part 33 may be designed in such a mannerthat the top thereof is located at a higher level than the top surfaceof the center disk part 31, and the bottom thereof is located at a lowerlevel than the bottom surface of the center disk part 31. The centerouter circumferential part 33 and the center inner circumferential part32 may correspond to each other. The center outer circumferential part33 and the center inner circumferential part 32 may be supported by thelower guide part 52 such that the positions thereof are maintained.

The center upper curved part 34 is formed at the top of the center diskpart 31, and brought into line contact with the upper case 10. Forexample, the center upper curved part 34 may have a plurality of curvedsurfaces, each of which is designed so that the top thereof is locatedat a higher level than the center inner circumferential part 32 and thecenter outer circumferential part 33. Thus, the center upper curved part34 may be brought into line contact with the upper cover part 11.

The center lower curved part 35 is formed at the bottom of the centerdisk part 31, and brought into line contact with the lower case 20. Forexample, the center lower curved part 35 may have a plurality of curvedsurfaces, each of which is designed so that the bottom thereof islocated at a lower level than the center inner circumferential part 32and the center outer circumferential part 33. Thus, the center lowercurved part 35 may be brought into line contact with the lower coverpart 21.

At this time, the center upper curved part 34 and the center lowercurved part 35 each have one or more cycloid surfaces. When the centerupper and lower curved parts 34 and 35 each have the cycloid surfaces,stress concentrated by a vertical load may be distributed.

A curved storage part 36 formed between the cycloid surfaces may store alubricant therein. That is, the connection point between the adjacentcycloid surfaces may correspond to the bottoms of the cycloid surfaces,such that a recess is formed therebetween, and a lubricant such asgrease is stored in such a recess.

At this time, the height (c) of the cycloid surface from bottom to topmay be set in the range of 10% to 50% of the height (d) of the centerplate 30. The height (d) of the center plate 30 may indicate thedistance between the top of the center upper curved part 34 and thebottom of the center lower curved part 35, and the height (c) of thecenter upper curved part 34 or the center lower curved part 35 frombottom to top may be defined as expressed by Equation 2 below.0.1d≤c≤0.5d  [Equation 2]

Through the ratio regulation of the heights of the center upper andlower curved parts 34 and 35 from bottom to top, two or more centerupper curved parts 34 and two or more center lower curved parts 35 maybe formed on the center disk part 31, and the plurality of curvedstorage parts 36 formed as grooves at the intersections between therespective curved surfaces may be filled with a lubricant. The lubricantstored in the curved storage part 36 can improve the lubrication effectto lower torque.

FIG. 8 is a diagram schematically illustrating an installation space inaccordance with an embodiment of the present disclosure. Referring toFIG. 8 , the rotation induction device 1 for a vehicle in accordancewith the embodiment of the present disclosure may further include aninstallation space 70. The installation space 70 may be formed betweenthe upper case 10 and the lower case 20, and formed as a ring-shapedspace into which the center plate 30 is to be inserted.

More specifically, the installation space 70 may indicate a space formedbetween the upper guide part 51 and the lower guide part 52. That is,the installation space 70 may correspond to the ring-shaped spacebetween the outer circumferential surface of the upper guide part 51 andthe inner circumferential surface of the lower guide part 52.

The volume (e) of the center plate 30 may be set in the range of 50% to98% of the volume (f) of the installation space 70. The volume (e) ofthe center plate 30 and the volume (f) of the installation space 70 maybe defined as expressed by Equation 3 below.0.5f≤e≤0.98f  [Equation 3]

The ratio regulation of the volume (e) of the center plate 30 mayregulate a change in position by a horizontal load so as to prevent alubricant leak due to a change in position or shock which is caused by ahorizontal load of the center plate 30, which makes it possible toimprove the durability and lubrication performance.

FIG. 9 is a diagram schematically illustrating an inflow prevention partin accordance with an embodiment of the present disclosure. Referring toFIG. 9 , the rotation induction device 1 for a vehicle in accordancewith the embodiment of the present disclosure may further include aninflow prevention part 80. The inflow prevention part 80 is formed onany one or more of the upper and lower cases 10 and 20, and serves toblock the inflow of foreign matters through the piston rod 200. Forexample, the inflow prevention part 80 may block foreign matters fromflowing into the gap between the upper case 10 and the piston rod 200and the gap between the lower case 20 and the piston rod 200.

More specifically, the inflow prevention part 80 includes an upperprevention part 81, a lower prevention part 82 and an inner preventionpart 83.

The upper prevention part 81 is extended downward from the inside of theupper case 10, and covers the piston rod 200. For example, the upperprevention part 81 may be integrated with the upper cover part 11, andextended downward from the inner circumferential surface of the uppercover part 11. The inner circumferential surface of the upper preventionpart 81 may cover the piston rod 200. The bottom of the upper preventionpart 81 may be located at a lower level than the bottom of the upperguide part 51.

The lower prevention part 82 is extended from the inside of the lowercase 20 so as to cover the piston rod 200, and disposed under the upperprevention part 81. For example, the lower prevention part 82 may beintegrated with the lower cover part 21, and formed in the lower coverpart 21. The inner circumferential surface of the lower prevention part82 may cover the piston rod 200. The lower prevention part 82 and theupper prevention part 81 may be disposed on a straight line. The topsurface of the lower prevention part 82 may be located at a lower levelthan the top surface of the lower cover part 21.

The inner prevention part 83 is extended upward from the lower case 20,and disposed to face the upper prevention part 81. For example, theinner prevention part 83 may be integrated with the lower cover part 21,and inserted between the upper prevention part 81 and the upper guidepart 51 so as to form a labyrinth structure. At this time, the top ofthe inner prevention part 83 may be located at a high level than thebottoms of the upper prevention part 81 and the upper guide part 51.

The distance (g) between the upper prevention part 81 and the lowerprevention part 82 may be set in the range of 10% to 50% of a height (h)of the upper prevention part 81. The height (i) of the upper case 10 maybe equal to or larger than the height (h) of the upper prevention part81.

That is, the height (h) of the upper prevention part 81 may indicate thelength of the upper prevention part 81 protruding from the bottomsurface of the upper cover part 11, and the height (i) of the upper case10 may indicate the thickness of the upper cover part 11. The heights(h) and (i) may be defined as expressed by Equation 4 below.0.1h≤g≤0.5h,h≤i  [Equation 4]

The regulation of the distance (g) between the upper prevention part 81and the lower prevention part 82 and the height (h) of the upperprevention part 81 may block the contact between the upper preventionpart 81 and the lower prevention part 82 and thus prevent reduction intorque. Furthermore, the inflow of foreign matters may be blockedthrough the labyrinth structure, which makes it possible to protect theequipment. Furthermore, the regulation of the height (i) of the uppercase 10 may block reduction in stiffness of the upper cover part 11.

In the rotation induction device 1 for a vehicle in accordance with theembodiment of the present disclosure, the center plate 30 may beinstalled in the installation space 70 formed between the upper case 10and the lower case 20, in order to regulate a change in position, causedby a horizontal load. Thus, the rotation induction device 1 may preventshock caused by the horizontal load of the center plate 30 or alubricant leak caused by a change in position.

Although exemplary embodiments of the disclosure have been disclosed forillustrative purposes, those skilled in the art will appreciate thatvarious modifications, additions and substitutions are possible, withoutdeparting from the scope and spirit of the disclosure as defined in theaccompanying claims. Thus, the true technical scope of the disclosureshould be defined by the following claims.

What is claimed is:
 1. A rotation induction device for a vehicle,comprising: an upper case formed of a synthetic resin material, andhaving a piston rod passing therethrough; a lower case formed of asynthetic resin material and disposed under the upper case, wherein thepiston rod passes through the lower case; a center plate formed of asynthetic resin material, disposed between the upper case and the lowercase such that the piston rod passes through the center plate, andconfigured to induce rotation of either one or both of the upper caseand the lower case, wherein the center plate comprises: a center diskpart, and a ring-shaped installation space disposed between the upperand lower cases, wherein the center plate is inserted in the ring-shapedinstallation space; wherein at least one cycloid surface is formed on atleast one of the upper case and the lower case and contacts the centerplate.
 2. The rotation induction device of claim 1, wherein the uppercase comprises: an upper cover part configured to cover a top of thecenter plate, the upper cover part having an upper hole formed in acenter thereof such that the piston rod passes through the upper hole,wherein the at least one cycloid surface is formed on the upper coverpart; and an upper blocking part disposed at an edge of the upper coverpart, and configured to block an inflow of foreign matter.
 3. Therotation induction device of claim 2, wherein the lower case comprises:a lower cover part configured to cover a bottom of the center plate, thelower cover part having a lower hole formed in a center thereof suchthat the piston rod passes through the lower hole, wherein the at leastone cycloid surface is formed on the lower cover part; and a lowerblocking part disposed at an edge of the lower cover part, andconfigured to block the inflow of foreign matter.
 4. A rotationinduction device for a vehicle, comprising: an upper case formed of asynthetic resin material, and having a piston rod passing therethrough;a lower case formed of a synthetic resin material and disposed under theupper case, wherein the piston rod passes through the lower case; acenter plate formed of a synthetic resin material, disposed between theupper case and the lower case such that the piston rod passes throughthe center plate, and configured to induce rotation of either one orboth of the upper case and the lower case, wherein the center platecomprises: a cycloid upper surface in contact with a lower surface ofthe upper case, and a cycloid lower surface in contact with an uppersurface of the lower case; and a ring-shaped installation space disposedbetween the upper and lower cases, wherein the center plate is insertedin the ring-shaped installation space.
 5. The rotation induction deviceof claim 4, wherein the upper case comprises: an upper cover partconfigured to cover a top of the center plate, the upper cover parthaving an upper hole formed in a center thereof such that the piston rodpasses through the upper hole; and an upper blocking part disposed at anedge of the upper cover part, and configured to block an inflow offoreign matter.
 6. The rotation induction device of claim 5, wherein thelower case comprises: a lower cover part configured to cover a bottom ofthe center plate, the lower cover part having a lower hole formed in acenter thereof such that the piston rod passes through the lower hole;and a lower blocking part disposed at an edge of the lower cover part,and configured to block the inflow of foreign matter.
 7. The rotationinduction device of claim 6, wherein the upper blocking part comprises:an upper blocking hook part extended downward from the edge of the uppercover part; and an upper blocking protrusion part protruding downwardfrom the upper cover part, and disposed to face the upper blocking hookpart.
 8. The rotation induction device of claim 7, wherein the lowerblocking part comprises: a lower blocking locking part disposed at theedge of the lower cover part, and including a groove to which the upperblocking hook part is locked and fixed; a lower blocking dropping partextended from the edge of the lower cover part toward a bottom of theupper blocking hook part and configured to drop foreign matter; and alower blocking protrusion part protruding upward from the edge of thelower cover part, and disposed between the upper blocking hook part andthe upper blocking protrusion part.
 9. The rotation induction device ofclaim 4, wherein the center plate comprises: a center disk part; acenter inner circumferential part formed on an inner circumferentialsurface of the center disk part; a center outer circumferential partformed on an outer circumferential surface of the center disk part; acenter upper curved part formed at a top of the center disk part, anddisposed in line contact with the upper case; and a center lower curvedpart disposed at a bottom of the center disk part, and disposed in linecontact with the lower case.
 10. The rotation induction device of claim9, wherein tops of the center inner circumferential part and the centerouter circumferential part are located at a level higher than a topsurface of the center disk part, and bottoms of the center innercircumferential part and the center outer circumferential part arelocated at a level lower than a bottom surface of the center disk part.11. The rotation induction device of claim 9, wherein the center uppercurved part and the center lower curved part each have one or morecycloid surfaces.
 12. The rotation induction device of claim 11, whereina lubricant is disposed in a curved storage part disposed between theone or more cycloid surfaces.
 13. The rotation induction device of claim4, wherein a volume of the center plate is 50% to 98% of a volume of theinstallation space.